%t is the time the TCP connection was accepted, in the default format. Same thing is available in GMT (%T) and local time (%Tl).
Quoting from MEDIUM: log: Decompose %Tq in %Th %Ti %TR:
In addition to this, we have new timestamps %tr, %trg and %trl, which
log the date of start of receipt of the request, respectively in the
default format, in GMT time and in local time (by analogy with %t, %T
and %Tl). All of them are obviously only available for HTTP. These values
are more relevant as they more accurately represent the request date
without being skewed by a browser’s preconnect nor a keep-alive idle
time.
Then what you need is %tr, %trg or %trl, depending on your format preference.